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Carrier-Mediated Transport of Folate in a Mutant of Pediococcus cerevisiae

Department of Bacteriology, The Hebrew University-Hadassah Medical School, Jerusalem, Israel

ABSTRACT

A mutant strain of Pediococcus cerevisiae (P. cerevisiae/PteGlu) was isolated which grows on low-folate (PteGlu) concentrations (200 pg/ml). The growth response of the parent and mutant strains to folinate (5-CHO-H₄PteGlu) was the same. The transport of ¹⁴C-PteGlu by P. cerevisiae/PteGlu was temperature-dependent (Q₁₀ between 27 C and 37 C was about 2), energy-dependent, and pH-dependent and was inhibited by iodoacetate, 2,4-dinitrophenol, potassium fluoride, and sodium azide. The uptake obeyed saturation kinetics with an apparent K_m of 6.6 x 10^–6 M and V_max of 4.0 x 10^–10 mol per min per mg (dry weight). At the steady state the intracellular concentration of PteGlu was 120-fold higher from that of the medium. Reduced folates like 5-CHO-H₄PteGlu and methyl-tetrahydrofolate (5-CH₃-H₄PteGlu) as well as 2,4-diaminoanalogues (amethopterin and aminopterin) were shown to compete for the PteGlue-carrier.

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